Adipate dianion

Compound 391 (in which the tosylate was substituted by methyl groups), which seemed to be less selective for carboxylate than 388 and 390, proved however to be a good receptor for the adipate dianion. No crystal structure of the resulting host-guest molecule could be obtained. However, a likely arrangement of the dicarboxylate unit in 391 based upon H NMR data is as represented in Figure 78. 

The addition of tetrabutylammonium adipate to electrochemical solutions of compound [86] led to a cathodic shift of 50 mV, suggesting that this receptor can electrochemically recognize this dianionic guest in acetone solution. Similar electrochemical experiments with other biscobaltocenium receptors gave inconclusive results because of solubility problems. 

Malonate and the dianions of the other aliphatic dicarboxylic acids H02 C(CH2 ) CO,H (n = 1-8) have been isolated as crystalline hydrates, and some of these have been dehydrated.293 X-Ray structural analyses have been reported for the malonate dihydrate,294 which has trans H2Os and bridging malonates of type (110), and for the succinate tetrahydrate and adipate dihydrate 295 the succinate reputedly has a trans- fAn02 (H2 0)4 ] polyhedron with bridging dicarboxylate, presumably as in (109). The monoanion of maleic acid (111) is only unidentate in crystalline [Mn(H-maleate)2-(H20)4] 296 but the equivalent compound of phthalic acid is a bis-chelated octahedral [Mn(0,0)2 (H2 0)2] species.297 Clearly other interactions in the solids, as well as the bonding interactions with Mn", define structure in the carboxylate compounds. 

Hi. Other dicarboxylic acids. Aqueous solutions of malonate CH2(C00 )2, adipate (CH2CH2COO )2, succinate (CH2COO )2 12, 573, 598), and mercaptosuccinate 516) with aqueous zirconium(IV) solutions leads to the precipitation of solids with composition [ZrO(CH2)K(COO )2]. The 1 1 adipate and succinate species do not dissolve in excess carboxylic acid solution indicating that the dianionic species are not formed. At metal ion concentrations of (1 to 2) x 10 M and hydrogen ion concentrations between 0.087-0.350 M, malonic and succinic acids establish the equilibrium defined by the equation... 

A very interesting report is for a trio of dicarboxylic acids, oxalic (C2H2O4), malonic (C3H4O4), and adipic (C6H10O4), all of which can lose two hydrogens on their way to forming a dianion [136]. Continuum... 

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